Fundamental Concepts in Organic Agriculture

Jonathan DeenikAssistant Specialist, Soil Fertility

Department of Tropical Plant and Soil Sciences

Soil Fertility WorkshopFebruary 23 & 24, 2005

Outline

• Definition• Historical Development and Philosophy• Principles• Nutrient Cycles -Soil Biology• Tools and Practices

Definition

“..an ecological production management system that promotes and enhances biodiversity, biological cycles and soil biological activity. It is based on minimal use of off-farm inputs and on management practices that restore, maintain and enhance ecological harmony.”

National Organic Standards Board

OriginsJ.I. Rodale coined the word “organic” (1940’s) and principal figure in U.S. organic agriculture.Rodale’s concepts drawn primarily from British agronomists Albert Howard

-“An Agricultural Testament” (1943)- “The Soil and Health” (1947)

- Natural approach to building soil fertility, return wastes to the soil

Lady Eve Balfour, “The Living Soil” (1948)- Ecological farming

Rachel Carson, “Silent Spring” (1962)

PhilosophyHuman health tied to the health of the environmentA healthy soil is the foundation“Feed the soil to feed the plant”

http://www.sct.embrapa.br/diacampo/2004/releases.htm

Guiding PrinciplesBiodiversity- Mimic nature, improve nutrient cycling, disease

suppression, tilth, and N fixation

Diversification and Integration- Integrating crop and livestock operations- Perennial and annual cropping systems

Sustainability- Reduce off-farm inputs- Enhance soil resource

Natural Plant Nutrition

Guiding PrinciplesNatural Plant Nutrition- Manage nutrients by managing soil organisms- Build the soil

Natural Pest Management- Pests are indicators of “…how far a system has strayed

from the natural ecosystem it seeks to imitate.”- Natural predators and the maintenance of a complex

agro ecosystem

Integrity- Protecting organic products from contamination and

commingling with non-organic products

Feed the Soil?

Feed the bugs!- Microorganisms

- Bacteria- Fungi- Actinomycetes- Protozoa- Algae

- Nematodes- Macrofauna

- Earthworms“The plow is one of the most ancient and most valuable of

man’s inventions; but long before he existed the land was I fact regularly ploughed, and continues to be thus ploughed by earthworms.”

Charles Darwin, 1881

http://universe-review.ca/R10-23-plants.htm

Nutrient CyclingSoil microorganisms mediate nutrient cycles through decomposition of organic residues- Microorganisms ‘feed’ on the residues- Biochemical by-products are plant nutrients (N,P,S)

and other beneficial compounds like humic acid

• Mineralization- Microbial conversion of organic N P and S into

ammonium, phosphate, and sulfate- Nutrients become available

• Immobilization- Microbial assimilation of inorganic N, P, and S- Nutrients temporarily tied up in microbial biomass

Mineralization/ImmobilizationC:N ratio>25-30net immobilizationN deficiency

C:N ratio < 25net mineralizationSource of plant N

Brady & Weil, 2004, Elements of the Nature and Properties of Soils

Factors Affecting Mineralization

1. Temperature

- Reaction ratesdouble with every10°C increase

30°C

19°C

12.5°C

De Neve et al., 2002

Factors Affecting Mineralization

2. Moisture- Mineralization low underdry conditions

- Increase to optimumunder moist conditions

- Decrease as soil becomes saturated

Source: Cassman & Munns, 1980

Microbial Functional GroupsBacteria- decomposers, primary players in NP and S

cycling- Actinomycetes act on more complex

compounds to form humusFungi- Decomposers, attack lignin- Nutrient acquisition (mycorrhiza)

Protozoa and Nematodes- Consume bacteria and fungi releasing plant

nutrients (N)- Activity increases decomposition rates

Factors Affecting Microbial Populations

Moisture- Microorganisms need water to survive

Oxygen- Bacteria both aerobic and anaerobic- Fungi, protozoa and nematodes aerobic

Temperature- Adaptable- Activity generally increases as temperature rises

Soil pH- Bacteria sensitive to acidity- Fungi function at low pH

Organic Matter- OM source of C and nutrients- OM additions stimulate microbial growth

Agricultural Practices Affecting Microbial Populations

Tillage- Destroys fungi, meso and macrofauna- Reduces OM- Reduces aggregation

Fertilizers- N and P fertilizers create acid zones killing

microorganisms

Fumigation- Indiscriminant destruction of microbial community

Monocropping- Reduces microbial diversity- Promotes pest build-up

What About the Soil Food Web?

http://www.magicsoil.com/MSREV2/soil_food_web.htm

What About the Soil Food Web?

Important to recognize the role of each functional group and their interdependenceRemember that management practices affect microbial interactionsSoil tests to quantify soil food web are expensive and difficult to interpretHot area for research

Tools and PracticesCrop Rotation

Soil fertility- Legumes for N fixation- Diverse rooting habits

Pest Management- Break pest cycles- Promote diversity

Know the family of the cropsCrops rotated so that crops from different families follow each other

Lettuce

Beans

Corn

Tomatoes

Tools and PracticesCrop Rotation

Crops rotated so that crops from different families follow each other

Example

Lettuce Beans Corn Tomatoes

Tools and PracticesGreen Manures in the Crop Rotation:

Soil fertility- Legumes for N fixation- Grasses for OM accumulation- Diverse rooting habits

Pest Management- Break pest cycles- Promote diversity, attract beneficials- Biofumigants (brassicas, sudan grass, sunn hemp)

Weed Management- Perennial rye- Oats

Tools and PracticesComposts and Manures:

Soil Conditioner- Feed the soil- Improve physical properties

Nutrient Availability- C:N ratio- Total N content- ≈ 15% of total N in mature composts available in the

first year (Bettina et al., 2003)- Field trials estimate that composts alone can satisfy

crop N demands after 40-80 years

Feather meal Dairy Manure CompostC:N ratio: 3.2 18 10-17Total N 12% 2.0% 1.0%

Tools and PracticesComposts and Manures:

Timing- Continuous additions to build up SOM- Mineralization potential of soil increases as

OM inputs increase with time- SOM acts as nutrient reserve continuously

releasing nutrients- High N materials can be used as a rapid

source of N in the short term

Tools and PracticesIntercropping and Companion Planting:

Interplanting 2 or more mutually beneficial plants to increase biodiversity

http://oregonstate.edu/dept/ncs/photos.html

Tools and Practices

Depends on managing beneficial insect predators/parasitesSeen as default benefit of organic soil management practices that promote above and below ground diversityCan include the release of control agentsFarmscaping: long/short term design to create habitats for beneficials

Biological Pest Control:

Tools and Practices

Tools for weed control, residue management, manure incorporation, hardpan destruction, pest controlNegative impacts:- Costly- Destroy humus reserves and soil organisms- compaction

Conservation and ridge tillage- Organic growers pioneers

Tillage and Cultivation:

Tools and Practices

Weed control, moisture and temperature control, soil organic matterLarge quantities of resistant organic materials (wood chips, straw, etc…)Not practical on a large scale

Mulching:

SummaryThe farm as an agro ecosystem- Balance through diversity- Crop and soil management based on understanding of

interactions within the ecosystem- Maximum yields not always the driving force

Careful management of soil organic matter the foundation to balance

Shift approach from treating the symptom to managing the system and all its components

Extension’s Role in Assisting Organic Growers

Understand and appreciate the fundamental approachUnderstand that organic farming operates on the same scientific principles governing any agricultural systemApply scientific principles within the agro ecological model embraced by many organic farmers

Soil and Tissue Testing for Organic Systems

Soil and tissue nutrient concentrations relevant for both conventional and organic systems

Plant nutrient availability governed by the same chemical and biological reactions regardless of farming systems

Remember the Important Role of Organic Matter in Soils

Physical- Improves aggregation (glue)- Improves water holding capacity (surface area)

Chemical- Increases nutrient availability (cycling, P and

micronutrient solubility- Increases CEC (200 cmolc kg-1)- Buffers the soil against pH changes

Biological- Increases microbial diversity- Assists in pathogen suppression

Remember the Important Role of Organic Matter in Soils

Physical- Improves aggregation (glue)- Improves water holding capacity (surface area)

Chemical- Increases nutrient availability (cycling, P and

micronutrient solubility- Increases CEC (200 cmolc kg-1)- Buffers the soil against pH changes

Biological- Increases microbial diversity- Assists in pathogen suppression

Measuring Management Impacts on Soil Organic Matter

Total C- Total C changes slow- 0.001 to 0.01% increase in SOM for every ton/a

Soluble C- Hot water soluble C sensitive to organic inputs

CEC- Small increases in soil C have significant impacts on CEC

Microbial biomass- Difficult procedure sensitive to climate and other

environmental factorsFunctional Groups- Expensive - Changes due to organic inputs or other factors?

Making Fertilizer Recommendations in Organic Systems

Determine crop rotationGet soil analysis- Same rules apply for pH, exchangeable cations and soil P- Interpreting total C and total N is difficult- 1-5% of N in SOM mineralized (12 - 60 lbs N/a)- Soils receiving lots of OM may have higher N mineralization

Obtain organic amendment chemical properties- C:N ratio- Total N

Hue & Silva, 2000

N Mineralization and Crop Nutrition

Excess N

N Deficiency

Source: Pang & Letey, 2000

Calculating Amendment Rate

Material: Blood meal (13% N)Crop N requirement: 150 lbs/aN release: High N content - rapid release (80%

available during the cropping system)Calculation: 150 lbs/(0.13*0.8) = 1,442 lbs/acre

Material: Chicken manure (3.0% N)Crop N requirement: 150 lbs/aN release: moderate N content - moderate release

(50% available during the cropping system)Calculation: 150 lbs/(0.03*0.5) = 10,000 lbs/acre

Nutrient Additions

P Inputs:- 3.5% P- (0.035*10,000lb) = 350 lb P per acre- Assume 40-50% of total P mineralizes- Can lead to P accumulation

K Inputs- Assume 90% of the K available- (0.9*0.021*10,000lb) = 189 lb K per acre

Manure ApplicationManure composed of Ammonia (10-30%) and organic NManure should be incorporated - 25% NH3 lost to volatilization after 1 day- 75% NH3 lost after a week

Information Gaps

Nutrient release form organic amendmentsImpact of green manure crops- Nutrients- Soil pathogens- weeds

Impact of soil management on pest/diseases

Next Steps

More Interaction with organic growersIncorporate lessons from the Mainland and EuropeA systems approach to research integrating soils, crops, plant pathology, entomology, and weeds

Resources

Books:Gershuny, G. and J. Smillie. The Soul of SoilLampkin, N. Organic FarmingColeman, E. The New Organic GrowerMagdoff, F. and H. van Es. 2000. Building

Soils for Better Crops. SustainableWeb:http://www.attra.org/organic.html